Video Clocked output and VGA

It looks like that you may have problems are with the SDRAM.

From what I see I think you are working with high clock rates for both the video and memory.

Your video clock is 70MHz while you need for composite input only 27MHz if the color components are parallel the VGA output (640 x 480 @ 60Hz) only need 25 MHz if the color components are parallel. 50 MHz clock for video will be OK.

The SRAM clock you use is 140MHz, but I think the SDRAM controller work only up to 100MHz in Stratix devices, in other device even less.

I would also suggest you to read in the SDRAM Controller document and follow the clock phase setting for the SDRAM.

Good luck,

Reuven